Rubberized abaca fiber paper



Patented Feb. 13, 1951 RUBBERIZED ABACA FIBER PAPER William A. Hermanson, Brookline, Mass.

No Drawing. Application April 23, 1948,

Serial No. 22,940

Claims. (c1.11'z 1ss) This invention relates to a manufactured sheet and to the art of making. such a sheet material of a fibrous structure combined with latices of the elastomeric type, together withwhich may be added as a part of the new invention a continuous phase film of particles derived from a dye-' stuff. I

More particularly, in accordance with the present invention, it is possible to make a relatively thin web of fibrous material of low density into one of high density without substantially changing the thickness of the web by impregnating it with elastomeric latices; such finished webs possessing great tensile strength, edge tear, elongation, and bursting strength.

In the prior art in the manufacture of artificial leather bases, shoe stay materials or the like, from paper webs impregnated with latices whether synthetic or natural, it is customary to employ paper webs comprising fibers of sulphite or sulphate pulp having absorbent characteristics. These webs are of compact formation, usually of calipers of .021 inch'or greater. The formation is created on-a paper machine and the interfiber orifices are from 0 to microns in diameter. When such webs are impregnated or saturated with latices, I have found that considerable resistance to the penetration of the rubber solids of the latex is encountered because these solids which range from one-tenth to onehalf micron, tend to aggregate before they have penetrated sufficiently or fiowed through the multiple strata of the paper web. The result is that the latex coagulates upon the upper and. uncler surface of the web, while the internal strata of the web remains virtually unimpregnated.

The initial tear strength of the web so saturated,

or impregnated is fairly good because the surface of the edge of the sheet is completely exposed for full impregnation, but once the tear has been started, the web gives way easily and the fibers of the internal strata, not having been intimately impregnated or saturated, are not bonded by the rubber solids, and tear at a comparatively low internal shearing strws. In brief, the internal tear resistance is extremely poor.

Latex dispersions further are sensitive systems, bein quickly coagulated by pressure, heat, cold or the presence of salts or electrolytes. When the latex is forced into the paper web, I have found also that the pressure used for forcing the latex into the web produces coagulation of the rubber solids on thesurfaces and the resulting film coalesced therefrom resists further penetration into the inner strata of the web. This condition results in low tensile strength, poor water V resistance, high initial edge tear but low edge tear after starting, poor elongation and low bursting strength.

' It is the purpose of this invention to greatly improve such artificial leather bases and shoe stay sheets, and to create a type which is far stronger and more resistant than any that has previously been available.

I have found that the following factors are critical in the making of stron sheetsv such as are used for strong artificial leather bases and in shoe stay sheets:

1. Fiber length. I

2. Sensitive absorbency- 3. Rapidity of penetration of latices through the webs.

4. Diameters of interfiber orifices.

5. Strengthening of the latex film with another film forming agent.

6. Incorporation of ultra violet resistance to promote aging strength.

Factors 5 and 6 are necessary particularly in such paper sheet for artificial leather bases and shoe stay materials since sheets now used lack water resistance and lose strength rapidly when exposed to sunlight.

I have found that a base sheet formed of uncontaminated, new or unused abaca fibers, free of hydrocarbon derivatives, botanically known as Musa textilis, having large interflber interstices of the order of 5 to microns, and lengths of 4 to 7 millimeters, with diameters of 17 to 25 microns, without any sizing or filler whatsoever, when impregnated or saturated with a properly prepared latex dispersion, Whether synthetic or natural, produces a sheet material of exceedingly high strength values of a measure never before achieved.

While the actual physical and chemical reaction, if any, does not seem to be entirely clear, it does seem that the uniform segmental fiber lengths, the substantial cylindrical cross sections of the fibers, their ability to deflocculate with substantial precision, plus other physical proper- 'ties of the abaca fiber bring about this remarkable result. These particular fibers in a pure state formed into sheets having large interfiber interstices permit the rubber solids of the latices to freely penetrate the sheet, surround all the fibers of the internal strata and enter freely and intimately into the cellular structure of the fibers themselves, and with a speed which insures that the latex is impregnated into the internal strata before it cancoagulate on the surfaces of the webs, the webs elongating throughout their in-.

ternal strata like rubber itself. Great tensile strength and fiexural edge tear is also obtained due to the combination of long fibers and rubber films attached thereto.

Another result of this combination is the increased quantitative mass of rubber solids that are retained in the web over what would be retained with other bases. In the conventional webs of sulphite and sulphate pulps, the maximum retention of rubber solids in the sheet is about 100 per cent. This ratio is conventionally established on the basis of the weight of the paper web before impregnation and the weight after impregnation and drying of the latex within the sheet and the evaporation of its liquid dispersion medium. For example, if a sheet of paper weighed 60 lbs. on the basis of 480 sheets, size 24 x 36 inches before impregnation with latex, it would bear a ratio of 100 per cent increase if it weighed 120 pounds on the same basis of 480 sheets after impregnation and evaporation of the liquid phase of the latex. The retained rubber solids and mineral matter would be equal to the base weight of the web of paper before treatment. This is expressed commercially by the phrase, "the sheet shows 100 per cent retention of solids," and will be so referred to hereinbelow, One hundred per cent retention of solids is approximately the maximum that has been possible in prior conventional sheets of paper because of the coagulation of latex at the surfaces of the sheet or other reasons as above set forth.

In my invention. I am easily able to produce sheets showing 165 per cent retention of solids with the resultant improvemgnt stemming therefrom. The high structural and physical values have been carefully measured and are shown in the following tables. The base weight of the shlet measured was 60 pounds per 480 sheets 24 x 36 inches before impregnation with latex. After impregnation and drying thoroughly the same sheet showed a weight of 159 pounds per 483 sheets, thus revealing a retention of rubber and mineral solids of 165 per cent. The sheet had a caliper of .015 inch.

This may be compared with a similar sulphite sheet wherein the base weight of 480 sheets 24" x 36" is 83.1 pounds before impregnation and after impregnation 166.2 pounds showing a retention oi rubber solids of 100%. The sheet 4 calipers .017 or slightly more than the similar sheet of the present invention.

Tested on strips-- 0 long 4%" long 5" long 6" Ian 3" wide )4" wide 1" wide 6 wi Tensile s3 3n, gfg Eltongagursiing e on trengt Point I oint Lbs./ Pounds Pounds Per cent sq. in. Grain Direction 63 18. 4 30 61 Transverse to Grain 57. 2 18.1

One of the further di iiiculties with previous latex film and paper web combinations has been the low resistance of the sheet against deterioration from water and sunlight.

the susceptibility of the water because of presence rubber particles and the sensitivity of rubber solids to ultra violet rays. I have found a means of improving these two characteristics by the introduction into the latices of a blue fiourescent dye which in small dilutions is virtuall colorless, showing only a pale violet color. This type of dye may be either a stilbene derivative, trlazinacr modified umbelliferone. When such a dye is mixed with water in small dilutions, boiled for five minutes and then poured in a thin layer into a shallow glass dish. evaporation of all the water discloses a thin film of continuous phase, having water resistance and substantial strength. Such dyes also absorb ultra violet light and emit the energy in the form of visible radiation. A solution of 5 grains to 100 milliliters of water upon impregnation into cellulosic materials shows a pale violet color, and is very resistant to discoloration by sunlight. I have utilized these properties by combining such a mixture of the dye with latex at 130 degrees Fahrenheit for ten minutes, whereupon the latex is intimately dyed therewith. Although other formulations may of soap fibers in the be made, and although it is not intended to limit the invention to the preferred formula set forth. I am s-tting forth the following as one which has been used by me in my laboratory tests to produce enhanced water resistance to the impregnated abaca web as well as resistance to discoloration by sunlight:

50 parts latex 40-50% solids 45 parts of solution of 5 grains of dye, of a stilbene derivative, triazine or modified umbelliferone, in ml. of water 5 parts glycerine The glycerine is added to the dye solution and this is added to the latex, which is heated on a slow plate to degrees Fahrenheit for ten minutes. impregnation with this formula into the abaca sheet shows marked water resistance as well as resistance to discoloration. It is possible to increase the actual dye content by using a more concentrate dye solution as, for instance, 10 grains to 100 ml. of water.

In using the word latex, I mean any colloidal system of natural rubber solids or synthetic emulsion polymers in the colloidal range which upon coagulation exhibit elastomeric properties.

In theformula given above the latex solution may be more or less concentrated, the main factor being obtaining the equivalent weight latex solids to the ratio of the other non-aqueous ma- These defects. are inherent in the latices themselves due to\ particles to take up terials. Sufficient water must, 'of course, be used so that the paper may be readily impregnated. Having now described my invention, I claim: 1. A method of preparing a flexible, yieldable. substantially non-stretchable sheet which comprises impregnating a web of new abaca fibers with a liquid comprising.

50 parts latex 4050% solids parts of a solution of 5 grains of dye of a stilbene derivative 5 parts glycerine whereby the sheet after drying thoroughly has a rubber and mineral solid retention of 165% of the base weight of the sheet before impregna tion.

3. A flexible, yieldable, substantially nonstretchable sheet comprising a pre-i'ormed paper web of new abaca fibers which has been impregnated with rubber latex so as to incorporate from to 165% of latex rubber therein, said web having interstices ranging from 5 to microns thereby increasing the latex solid retention to a magnitude from 100 to by weight of the sheet before impregnation.

3. A flexible, yieldable, substantially non- 6 stretchable sheet comprising a porous pre-formed paper web of new abaca fibers which has been impregnated with rubber latex so as to incorporate from 100 to 165% of the rubber latex therein, thereby increasing the latex solid retention to a magnitude from 100 to 165% by weight of the sheet before impregnation.

4. A sheet as in claim 3 which has been impregnated with latex in which a blue fluorescent dye has been incorporated.

5. A sheet as in claim 3 which has been impregnated with latex in which adye of a stilbene derivative has been incorporated.

WILLIAM A. HERMANSON.

mwnmmcrzs crren The following references are of record in the file of this patent:

UNITED STATES PATENTS 

2. A FLEXIBLE, YIELDABLE, SUBSTANTIALLY NONSTRETCHABLE SHEET COMPRISING A PRE-FORMED PAPER WEB OF NEW ABACA FIBERS WHICH HAS BEEN IMPREGNATED WITH RUBBER LATEX SO AS TO INCORPORATE FROMM 100 TO 165% OF LATEX RUBBER THEREIN, SAID WEB HAVING INETESTICES RANGING FROM 5 TO 150 MICRONS THEREBY INCREASING THE LATEX SOLID RETENTION TO A MAGNITUDE FROM 100 TO 165% BY WEIGHT OF THE SHEET BEFORE IMPREGNATION. 